This paper aims to widen the history of blood disease research beyond sickle cell anemia, situating it at the intersection of US racial politics and public health, and international malaria eradication campaigns in the Third World. It focuses on studies of G6PD deficiencies in the Mixtecos of the Mexican Pacific coast, and the Lacandones of the Mayan region in Chiapas. Two medical geneticists, Rubén Lisker and James E. Bowman, developed research projects that engaged these populations, looking for answers to evolutionary, biomedical, and genetics questions. Their practices and the context of knowledge production about these indigenous groups—how they were made objects of inquiry and intervention (Populations of Cognition)—are in full view in both cases. 1

We develop the concept of “Populations of Cognition” in order to generate new insights into the complex dynamics that have made certain human groups integral to the production of scientific knowledge in and about Latin American. In this introduction, we define the concept of Populations of Cognition by reflecting on the six empirical papers that comprise this special issue. Across these papers, Populations of Cognition emerge as sociotechnical constructions defined in the context of scientific practice, they are often ascribed meaning according to particular western imaginaries about the region and its people, and, charged with this meaning, they can ultimately become a cognitive tool, facilitating particular ways of scientific reasoning, learning, and experimentation. Our examination of practices of inquiry into human populations in Latin America further centers the region as a key site of knowledge making with important geopolitical implications in the decades following World War II and to the present.